Abstract

Middle-ear sound transmission was evaluated as the middle-ear transfer admittance (the ratio of stapes velocity to ear-canal sound pressure near the umbo) in gerbils during closed-field sound stimulation at frequencies from , a range that spans the gerbil’s audiometric range. Similar measurements were performed in two laboratories. The magnitude (a) increased with frequency below , (b) remained approximately constant with frequency from , and (c) decreased substantially from . The phase increased linearly with frequency from , consistent with a delay, and flattened at higher frequencies. Measurements from different directions showed that stapes motion is predominantly pistonlike except in a narrow frequency band around . Cochlear input impedance was estimated from and previously-measured cochlear sound pressure. Results do not support the idea that the middle ear is a lossless matched transmission line. Results support the ideas that (1) middle-ear transmission is consistent with a mechanical transmission line or multiresonant network between 5 and and decreases at higher frequencies, (2) stapes motion is pistonlike over most of the gerbil auditory range, and (3) middle-ear transmission properties are a determinant of the audiogram.

The authors thank Elizabeth Olson, Wei Dong, Ombeline de la Rochefoucauld, and Willem Decraemer for many helpful discussions, and William Peake, Melissa Wood, Kelly Brinsko, Heidi Nakajima, and the staff of the Eaton-Peabody Laboratory for greatly appreciated assistance. This work was supported by NIDCD R01-DC00194 (M.E.R. and J.J.R.) and The Royal Society and the Wellcome Trust (N.P.C.).